1. Technical Field
The present invention relates to television tuners and more particularly pertains to a highly integrated television tuner fabricated on a single microcircuit device.
2. Background Art
In the past, television tuners have been constructed to be fairly complex and typically include between 100 and 200 elements on a circuit board. One example of a prior art tuner is shown in Prior Art FIG. 1. In such Figure, a tuner 100 is shown to include, at the most basic level, an upconverter 102, an upconverter output circuit 104, an intermediate filter circuit 106, a downconverter 108, and an output filter 110.
The upconverter 102 takes the form of an integrated circuit, i.e. ACU50751. In use, the upconverter 102 mixes an input signal with a reference signal to generate an intermediate frequency signal. Typically, such intermediate frequency signal is in the order of 1.2 GHz. Connected to the upconverter 102 is the output circuit 104 which includes a balun 111, or balancing transformer, for converting the intermediate frequency signal from the upconverter 102 to a single-ended form.
The downconverter 108 of the tuner 100 is connected to the upconverter output circuit 104 with the intermediate filter circuit 106 connected therebetween. Finally, the output filter 110 is connected to the downconverter 108 for filtering purposes. During operation, the downconverter 108 mixes the intermediate frequency signal with a reference signal to generate a second intermediate frequency signal usually in the order of 44 or 36 MHz.
Due to the specific values of the first and second intermediate frequency signals, image frequencies are generated at 1.2 GHz+/xe2x88x9288 or 72 MHz. These image frequencies, in turn, require complex filtering. For example, intermediate filter circuit 106 requires a pair of filters 112 having an interstage buffer 114. Further, the output filter 110 must consist of an intricate SAW filter or the like.
It should be noted that both of the foregoing filters are extremely difficult, if not impossible, to implement on an integrated circuit in view of high xe2x80x9cQxe2x80x9d ratings. As such, the tuner 100 of Prior Art FIG. 1 must be implemented with multiple discrete components. There is thus a need in the prior art for a tuner with simplified filtering requirements and the capability of being implemented on a single integrated circuit.
A television receiver is provided including a first mixer having a first input adapted for receiving an input signal in a predetermined frequency range. It should be noted that the input signal may take the form of either a broadcast television signal, a cable television signal, or a digital signal transmitted over a cable delivery system. The first mixer further includes a second input adapted for receiving a first reference signal having a first operating frequency. In use, the first mixer is suitable for outputting an intermediate frequency signal having a frequency greater than at least one frequency in the predetermined frequency range. Also included is a filter for filtering the intermediate frequency signal. A phase shifting network is provided which includes an input adapted for receiving a second reference signal having a second operating frequency. The phase shifting network further includes a pair of outputs. In operation, the phase shifting network is suitable for outputting a pair of quadrature reference signals each having a frequency substantially equal to the second operating frequency. A pair of second mixers each have a first input coupled to the filter and a second input coupled to one of the outputs of the phase shifting network. Coupled to the second mixers are a pair of low-pass filters for filtering the output signals. In use, the second mixers serve for generating output signals that are in quadrature and at a baseband frequency for being processed by a subsequent digital signal processor.
By this structure, the stringent requirements associated with filtering the intermediate frequency signal is avoided by downconverting the intermediate frequency signal to a baseband frequency. As such, the filter of the present invention that follows the first mixer may be simplistic in design since image frequencies are not produced. The simplistic nature of the filter in turn allows easier implementation on an integrated circuit with the remaining components of the present invention. Further, the low-pass filters may also be implemented on the integrated circuit since an intricate SAW filter is not required.